In recent years, pheromones have acquired great importance in the research for methods for the control of insects noxious to agricultural cultivations.
The pheromones are secreted on the outer surface of the insect body and, depending on the type of reaction that they induce, may be subdivided into: aggregating, tracing or marking, sexual, or alarming pheromones, or they may be of other types.
The diffused and interesting pheromones, due to the application possibilities in the control of insects, are the sex pheromones which are secreted more frequently by the females, but also by the males, and which attract the individuals of the opposite sex for the mating. The use of the pheromones for the control of the insects is actually based on the principle that small quantities of such compounds, obtained by synthesis, will cause the same reactions as those induced by the male or female insect which secrete the natural attractants (pheromones).
Practically, the synthetised sex pheromones are applied both for monitoring the growth of the populations of the noxious species, as well as for controlling the harmful species by hindering the matings (mating disruption).
In the latter case, the sex pheromones have the task of either partially or completely substituting the insecticides and of directly controlling the insects by modifying their behavior.
The techniques used for achieving this purpose are two: mass trapping and confusion. The first, (mass trapping), has for its aim the attraction to, and catching in, small trapping cages of the greatest possible number of insects. The second, (confusion method), consists in diffusing the pheromones in the air so as to incapacitate the males or females to "feel" and "locate" the individuals of the opposite sex, thus hindering the mating.
In practice, the attractant may be diffused by distributing the product at various points in suitably distanced zones, or by nebulizing the product uniformly over the whole cultivation.
In the first instance, use is made of evaporators in which the pheromones are englobated or incorporated into substances of different nature, suited for causing the volatilization at a suitable rate and persistance. However, such systems are rather expensive due to the high cost of the evaporators and of labor.
A less expensive and elaborate system consists in distributing the pheromone over the whole zone by nebulizing it both from the ground and from aircraft, and by having recourse to special formulations with controlled release.
A number of known slow-release formulation systems may consist of aqueous suspensions of pheromone-containing microcapsules having walls made of polyamides (U.S. Pat. No. 3,577,515) or of gelatin (U.S. Pat. Nos. 2,800,457; 2,800,458), or they may consist of pheromone englobating multi-layer polymeric systems (A.C.S. 33-1976, pg. 283) or of hollow fiber systems consisting of capillaries with an open end through which the pheromone volatilizes (U.S. Pat. No. 4,017,030).
Such systems require a special elaboration both as far as concerns preparation thereof and, above all, for the successive distribution in the field.
A further drawback of some of those systems consists in supplying a release kinetics of the pheromone that is not linear, just due to the construction of the capsule itself.
The rate at which the pheromone is released is not only affected by the quantity of the pheromone, by the chemical composition of the capsules and by the chemical composition of the other formulation components, but also by environmental factors such as temperature, light and moisture.
A desired requisite for a formulation that will release a sufficient quantity of pheromone to permeate the air and achieve the effect of inhibiting the mating, is a controlled total and constant release for an adequate period of time.